1. Field of the Invention
The present invention relates to wheelchairs. More specifically, the present invention relates to manually powered wheelchairs.
While the present invention is described herein with reference to a particular embodiment for an illustrative application, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teaching provided herein will recognize additional modifications, applications and embodiments within the scope thereof.
2. Description of the Related Art
Conventional manual wheelchairs have a rim, concentric to the wheel, by which the occupant manually propels the wheelchair. The hands of the wheelchair occupant apply a frictional force to the rim of the wheelchair to stop or slow the wheelchair.
There are several shortcomings associated with conventional manual wheelchairs. An occupant of a conventional wheelchair must typically expend considerable energy to travel on rough terrain or up hills and ramps. On steep ramps, the force required for propulsion or stopping may exceed the strength or stamina of the occupant. Stopping or slowing wheelchairs of current design can be quite difficult and trips of long distances may result in considerable fatigue.
Further, the rim of the wheelchair may be at a high or a low temperature extreme, depending on the weather conditions. In addition, the hands of the wheelchair occupant may become soiled as the wheels of the wheelchair are typically contaminated by dirt, oil, debris and even animal feces from the sidewalks, streets and other surfaces over which the wheelchair rolls. This is unsightly, uncomfortable, unsanitary and could lead to infection.
In propelling a wheelchair of current design, the user must often pivot his or her body forward. This may cause the loss of horizontal lap stability making it difficult to travel with objects such as a cup of coffee or a tray of food on one's lap.
While motorized wheelchairs address these problems, motorized wheelchairs are expensive, difficult to transport from location to location and virtually impossible for the wheelchair user to unload without the aid of another individual or expensive mechanical equipment. Also, the use of a motorized wheelchair typically results in muscle atrophy of the wheelchair occupant, and thus further disability.
There is therefore a recognized need in the art for a manual or non-motorized mechanism for wheelchairs which provides a mechanical advantage over the current wheelchair designs. Ideally, the mechanism will permit the wheelchair occupant to propel the wheelchair over varied terrain and distances, while the hands of the occupant remain clean and comfortable.
Preferably, the mechanism would offer a variable mechanical advantage whereby the ratio of wheel movement to arm movement can be one-to-one or selected to be different from one-to-one depending on the nature and grade of the terrain as well as the stamina and strength of the wheelchair occupant. For example, the mechanism would permit a ratio of wheel movement to arm movement of less than the one-to-one ratio of conventional wheelchairs for travel up hills, ramps and other terrain that is typically difficult to traverse such that the momentary effort required by the occupant of the wheelchair is greatly reduced from that required in a wheelchair of conventional design. Similarly, a ratio of greater than one-to-one could be chosen for faster travel than is possible with wheelchairs of current design over that terrain which is generally easy to cross. In addition, a neutral position could be provided such that the wheel receives no rotational force from movement of the mechanism.
There is a further need for a wheelchair braking mechanism which will allow the wheelchair occupant to effectively stop or slow the wheelchair more easily than is possible in a wheelchair of current design, while keeping the hands of the occupant clean, comfortable and safe from harm. There is a special need for such a braking mechanism where long ramps or steep walk ways are encountered, or whenever greater stopping force is required.